Current satellite pre-operational timelines can range from years to over a decade, depending upon the complexity and scope of a given system and its mission. For new concepts, this is incompatible with requirements to operate in space in a more responsive fashion. The extended developmental timeline results in obsolescence and cost/schedule increases of satellites, and since most satellites are unique and “one of a kind”, they require case-specific design, analysis, and qualification. With significantly shorter proposed timelines for responsive missions, there is little to no time available for design/assembly errors to be inferred from failed environmental testing. These tests typically include component and system exposure to thermal vacuum cycling, random vibration and shock loads, and flash x-ray. Realistically, an ideal responsive schedule comprises building modular systems from qualified components in such a way that few structural interfaces between connected validated components would exist as a source of uncertainty. These final interfaces then are the only areas in need of structural qualification.
Extensive research, specifically on feature extraction for satellite interfaces, has been explored and demonstrated using Structural Health Monitoring (SHM) systems and techniques as an enabling technology for responsive goals. Research has proven the feasibility of using embedded piezoelectric wafer active sensors (PWAS) to detect, localize, and quantify preload loss at bolted interfaces in a non-destructive manner. These kinds of systems are disclosed in, for example, U.S. Patent Application Publication No. 2011/0138918, “Structural Health Monitoring; an Enabler for Responsive Satellites”, Arritt et al., Proc. SPIE, Vol. 6935 (Mar. 10, 2008), and “Health Monitoring of Bolted Joints via Electrical Conductivity Measurements”, Argatov et al., International Journal of Engineering Science, Jun. 26, 2010. All of these documents are herein expressly incorporated by reference, in their entirety. One particular method uses piezoelectric wafers to both excite an elastic wave and to receive it. Two of these wafers are bonded to a structure. The source piezo is excited with an electric pulse which converts the electrical signal into mechanical displacement and creates a pressure and shear wave in the substrate that propagates radially outwardly from the center of the piezo. As the wave interacts with a feature (crack, hole, edge, thickness change, interface, stressed region, etc.), the waveform will change in amplitude, shape, or frequency. When the wave reaches the second piezo sensor, the wave is converted back into an electrical signal. If some change has occurred in the structure, the new wave propagation signal will show a proportionate change from the baseline signal.
Thermal conductance for space applications can currently only be accurately measured in a thermal vacuum chamber, and requires that no atmosphere be present. Heat sources and sinks are used to create thermal gradients across an area of interest. Thermal sensors are then placed along the path of thermal transition of interest to evaluate the change of temperature across the region and define the thermal gradient for that region. These measurements are done on both sides of an interface, as close as possible to that interface to verify that the thermal gradient across that interface is within acceptance of that required for thermal management. This test can take weeks to months and cost thousands of dollars.
What is needed, therefore, is a system and method for evaluating thermal conductance for space applications without the need to create an evacuated environment, with its attendant costs and delays.